An optical matrix switch includes one or more optical switches provided on optical waveguides connected to plural light signal input terminals and plural light signal output terminals. In this optical matrix switch, a light signal supplied to one of the input terminals is transmitted to a selected light signal output terminal by controlling the switching operation of the optical switches.
One type of such an optical switch is an optical directional coupler which comprises, for instance, two optical waveguides having two input terminals and two output terminals, and control electrodes for applying an electric field across the optical waveguides, respectively, provided on an optoclectrical crystal substrate such as LiNbO.sub.3, LiTaO .sub.3, etc. In this optical directional coupler, the switching of a light signal supplied to one of the two input terminals is carried out to be obtained at one of the two output terminals by controlling a voltage applied across the control electrodes.
Another type of an optical matrix switch is described in a report "Wideband optoelectronic matrix switch" included in the technical material OQE80-90, 1980 of "The Institute of Electronics Informations and Communications Engineers". In this optical matrix switch, the signal switching is carried out at a position where a light signal is converted to an electric signal.
A further type of an optical matrix switch is described in a report "Study of tunable optical connection by matrix driving on VSTEP devices" included in the technical material OQE 89-77, 1989 of "The Institute of Electronics Information and Communications Engineers". In this optical matrix switch, the signal switching is carried out at a position where an electric signal is converted to an optical signal.
According to the above three types of the optical matrix switches, however, there are disadvantages as set out below.
In the first optical matrix switch, high fabrication precision is required to decrease cross-talk tending to occur in normal operation, and a control voltage is required to be as high as 40 to 50 V.
In the second optical matrix, an electric output signal is required to be converted to an optical signal so as to realize the switching of light to light.
In the third optical matrix switch, an optical input signal is required to be converted to an electric signal so as to realize the switching of light to light.
As a result, the optical matrix switches of the second and third types become large in size, and low in operation speed.